As a semiconductor device capable of operating at low loss and high temperature, for instance, a device based on silicon carbide (SiC) has been drawing attention. Compared with silicon (Si), silicon carbide (SiC) has superior material properties, such as three times wider band gap, approximately times larger breakdown electric field strength, and approximately three times higher thermal conductivity.
In a MOSFET (metal oxide semiconductor field effect transistor) based on SiC, hydrogen termination is applied to the surface of a SiC substrate. Then, an insulating film made of
SiO2 is formed on the SiC substrate by surface oxidation or insulating film deposition.
In a MOSFET based on a substrate of SiC of the 4H structure (4H—SiC), the mobility at the interface between the SiC substrate and the insulating film made of SiO2 is very small.
Various modifications have been made to the insulating film and the interface only to obtain a low mobility (less than 100 cm2/Vs) far from the intrinsic characteristics of 4H—SiC (1000 cm2/Vs).
To form a channel of the MOSFET, aluminum (Al) as p-type dopant is introduced by ion implantation and the like. In this case, a certain large amount needs to be introduced to obtain a high breakdown voltage. However, an excessively large amount of introduction results in increasing the threshold and incurs the decrease of mobility. In a semiconductor device, it is important to obtain high breakdown voltage and stable threshold.